Out-of-equilibrium photon production in the late stages of relativistic heavy-ion collisions

In this work, we assess the importance of nonequilibrium dynamics in the production of photons from the late stages of relativistic heavy-ion collisions. The pT-differential spectra and v2 of photons from the late hadronic stage are computed within a nonequilibrium hadron transport approach, and compared to the results of a local equilibrium evolution using ideal relativistic hydrodynamics. It is found that nonequilibrium dynamics enhance the late-stage photon production at low pT and decreases it at higher pT compared to the estimate from hydrodynamics. This same comparison points to a significant increase in the momentum anisotropies of these photons due to nonequilibrium dynamics. Once combined with photons produced above the particlization temperature in the hydrodynamics evolution, the differences between the two approaches appear modest for the pT differential spectra, but are clearly noticeable at low pT for the elliptic flow: nonequilibrium dynamics enhance the photon v2 below pT ???1.4 GeV.